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Posted by HeatPro on November 15, 2008 at 11:48:08:
In Reply to: Re: installed outdoor thermostat for 2nd stage burner posted by Dave on November 15, 2008 at 10:27:03:
: My wife seems to disagree with all this. Her reasoning is that with the Ergomax tank and 70+ gallons of water in the system, that it would be better to run both burners to heat that mass of water quicker.
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: My line of thinking is that it is better to have one burner run longer than have 2 be on for a shorter time.
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: She seems to think that it is the same gas usage whether you run the 2 burners for a shorter time or one for a longer time.
+++ She is right when eliminating the mass of the hot water and metal in the heater that is giving off heat during the off period when the circulator isn't running (to get rid of the heat to the rooms, instead of using the heat to heat the basement.) She is also right if the boiler is set up to burn more efficiently at high fire than low fire. Your copper-tube boiler still holds a lot of heated water, even though it isn't as much as a cast or steel boiler.
The reason a boiler is matched to the heat load of the house is that the burners in an oversized heater cycle more frequently, increasing stand-by losses. True, they will shut off when the thermostat says to, but there's a lot more heat in a larger boiler left over that doesn't get to the rooms then. A low-mass variable input boiler has less of that.
There isn't a one-choice-fits-all answer. One-liners are good for comedy.